Signal Presence Detectors?

[Tony Allgood]

Another nice way to switch LEDs is to use a simple current sink, one
transistor, two Rs and one diode. This can supply current to a whole
load of LEDs in series. A simple NPN transistor in parallel with each
LED can turn the LED on or off. This has two advantages, reduces current
surges, and reduces current by running up to 10 LEDs off the rails.
Disadvantage: you need to carefully plan your on and off control
voltages to make sure each shunt transistor is fully turned off and on.

Regards,

Tony Allgood  Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan